The developmental physiology of the sporogonic stages of the malaria parasite will be studied, with particular reference to developmental changes in its energy metabolism and in its nucleus. Host-parasite relationships at different stages of development will be investigated, including factors which determine whether mosquitoes will be susceptible or refractory to the parasites and factors determining invasiveness of the sporozoite to the mosquito salivary gland, and the liver of its mammalian host. Electron microscopic, cytochemical, autoradiographic and biochemical procedures will be used. It is hoped that these investigations will increase our understanding of the development and physiology of the malaria sporozoite, and its relationship to its mosquito and mammalian hosts. Such knowledge may ultimately lead to a better understanding of the action of antimalarial drugs, effective vaccination procedures against sporozoite-induced malaria, cytogenetics of the parasite and the role of the parasite in inducing host pathology.